A magnetic pattern detection device for detecting a magnetic pattern of a medium which is carried along a medium feeding face has been known which includes a magnet structured to magnetize the medium and a magnetic sensor device structured to read a magnetic pattern of the medium that is magnetized by the magnet. The magnetic sensor device (magnetic pattern detection device) described in Japanese Patent Laid-Open No. 2009-163336 includes a plate-shaped sensor core made of a magnetic body such as amorphous metal or permalloy, and a coil wire is wound around the sensor core to structure an exciting coil for generating a bias magnetic field and a detection coil for detecting the magnetic pattern.
In the above-mentioned Patent Literature, one of end faces of the sensor core is a sensing face (magneto-sensitive face) of the magnetic sensor device and the sensing face is disposed on the same plane as the medium feeding face. In order to detect the magnetic pattern of a medium with a high degree of accuracy, it is preferable that a distance between the sensing face and a medium is set to be small for increasing the sensor sensitivity. Therefore, the end part on a medium side of the sensor core is commonly cut or ground for adjusting a length of the end part and a distance between the sensing face and a medium is set to be an optimum dimension.
However, a cutting work or a grinding work as described above is performed on an end part on a medium side of the sensor core, variation is occurred in the dimension of the sensor core due to the work and the magnetic circuit is varied. Therefore, the sensor characteristics such as the sensor sensitivity or the current efficiency are varied depending on the variation of the dimension of the sensor core and the stable sensor characteristics are not obtained.